package com.wechat.third.util.crypto;

import org.apache.commons.codec.binary.Base64;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.xml.sax.InputSource;

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import java.io.StringReader;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.util.Arrays;
import java.util.Map;
import java.util.Random;

/**
 * <pre>
 * 对公众平台发送给公众账号的消息加解密示例代码.
 * Copyright (c) 1998-2014 Tencent Inc.
 * 针对org.apache.commons.codec.binary.Base64，
 * 需要导入架包commons-codec-1.9（或commons-codec-1.8等其他版本）
 * 官方下载地址：http://commons.apache.org/proper/commons-codec/download_codec.cgi
 * </pre>
 */
public class WechatCryptUtil {

	private static final Base64 BASE64 = new Base64();
	private static final Charset CHARSET = StandardCharsets.UTF_8;

	private static final ThreadLocal<DocumentBuilder> BUILDER_LOCAL = new ThreadLocal<DocumentBuilder>() {
		@Override
		protected DocumentBuilder initialValue() {
			try {
				return DocumentBuilderFactory.newInstance().newDocumentBuilder();
			} catch (ParserConfigurationException exc) {
				throw new IllegalArgumentException(exc);
			}
		}
	};

	static {
		String errorString = "Failed manually overriding key-length permissions.";
		int newMaxKeyLength;
		try {
			if ((newMaxKeyLength = Cipher.getMaxAllowedKeyLength("AES")) < 256) {
				Class c = Class.forName("javax.crypto.CryptoAllPermissionCollection");
				Constructor con = c.getDeclaredConstructor();
				con.setAccessible(true);
				Object allPermissionCollection = con.newInstance();
				Field f = c.getDeclaredField("all_allowed");
				f.setAccessible(true);
				f.setBoolean(allPermissionCollection, true);
				c = Class.forName("javax.crypto.CryptoPermissions");
				con = c.getDeclaredConstructor();
				con.setAccessible(true);
				Object allPermissions = con.newInstance();
				f = c.getDeclaredField("perms");
				f.setAccessible(true);
				((Map) f.get(allPermissions)).put("*", allPermissionCollection);
				c = Class.forName("javax.crypto.JceSecurityManager");
				f = c.getDeclaredField("defaultPolicy");
				f.setAccessible(true);
				Field mf = Field.class.getDeclaredField("modifiers");
				mf.setAccessible(true);
				mf.setInt(f, f.getModifiers() & ~Modifier.FINAL);
				f.set(null, allPermissions);
				newMaxKeyLength = Cipher.getMaxAllowedKeyLength("AES");
			}
		} catch (Exception e) {
			throw new RuntimeException(errorString, e);
		}
		if (newMaxKeyLength < 256){
			throw new RuntimeException(errorString); // hack failed
		}

	}

	protected byte[] aesKey;
	protected String token;
	protected String appidOrCorpid;

	public WechatCryptUtil() {
	}

	/**
	 * 构造函数
	 *
	 * @param token          公众平台上，开发者设置的token
	 * @param encodingAesKey 公众平台上，开发者设置的EncodingAESKey
	 * @param appidOrCorpid  公众平台appid/corpid
	 */
	public WechatCryptUtil(String token, String encodingAesKey,
						   String appidOrCorpid) {
		this.token = token;
		this.appidOrCorpid = appidOrCorpid;
		this.aesKey = Base64.decodeBase64(encodingAesKey + "=");
	}

	static String extractEncryptPart(String xml) {
		try {
			DocumentBuilder db = BUILDER_LOCAL.get();
			Document document = db.parse(new InputSource(new StringReader(xml)));

			Element root = document.getDocumentElement();
			return root.getElementsByTagName("Encrypt").item(0).getTextContent();
		} catch (Exception e) {
			throw new RuntimeException(e);
		}
	}

	/**
	 * 将一个数字转换成生成4个字节的网络字节序bytes数组
	 */
	private static byte[] number2BytesInNetworkOrder(int number) {
		byte[] orderBytes = new byte[4];
		orderBytes[3] = (byte) (number & 0xFF);
		orderBytes[2] = (byte) (number >> 8 & 0xFF);
		orderBytes[1] = (byte) (number >> 16 & 0xFF);
		orderBytes[0] = (byte) (number >> 24 & 0xFF);
		return orderBytes;
	}

	/**
	 * 4个字节的网络字节序bytes数组还原成一个数字
	 */
	private static int bytesNetworkOrder2Number(byte[] bytesInNetworkOrder) {
		int sourceNumber = 0;
		for (int i = 0; i < 4; i++) {
			sourceNumber <<= 8;
			sourceNumber |= bytesInNetworkOrder[i] & 0xff;
		}
		return sourceNumber;
	}

	/**
	 * 随机生成16位字符串
	 */
	private static String genRandomStr() {
		String base = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
		Random random = new Random();
		StringBuilder sb = new StringBuilder();
		for (int i = 0; i < 16; i++) {
			int number = random.nextInt(base.length());
			sb.append(base.charAt(number));
		}
		return sb.toString();
	}

	/**
	 * 生成xml消息
	 *
	 * @param encrypt   加密后的消息密文
	 * @param signature 安全签名
	 * @param timestamp 时间戳
	 * @param nonce     随机字符串
	 * @return 生成的xml字符串
	 */
	private static String generateXml(String encrypt, String signature,
									  String timestamp, String nonce) {
		String format = "<xml>\n" + "<Encrypt><![CDATA[%1$s]]></Encrypt>\n"
				+ "<MsgSignature><![CDATA[%2$s]]></MsgSignature>\n"
				+ "<TimeStamp>%3$s</TimeStamp>\n" + "<Nonce><![CDATA[%4$s]]></Nonce>\n"
				+ "</xml>";
		return String.format(format, encrypt, signature, timestamp, nonce);
	}

	/**
	 * 将公众平台回复用户的消息加密打包.
	 * <ol>
	 * <li>对要发送的消息进行AES-CBC加密</li>
	 * <li>生成安全签名</li>
	 * <li>将消息密文和安全签名打包成xml格式</li>
	 * </ol>
	 *
	 * @param plainText 公众平台待回复用户的消息，xml格式的字符串
	 * @return 加密后的可以直接回复用户的密文，包括msg_signature, timestamp, nonce, encrypt的xml格式的字符串
	 */
	public String encrypt(String plainText) {
		// 加密
		String encryptedXml = encrypt(genRandomStr(), plainText);

		// 生成安全签名
		String timeStamp = Long.toString(System.currentTimeMillis() / 1000L);
		String nonce = genRandomStr();

		String signature = SHA1.gen(this.token, timeStamp, nonce, encryptedXml);
		return generateXml(encryptedXml, signature, timeStamp, nonce);
	}

	/**
	 * 对明文进行加密.
	 *
	 * @param plainText 需要加密的明文
	 * @return 加密后base64编码的字符串
	 */
	protected String encrypt(String randomStr, String plainText) {
		ByteGroup byteCollector = new ByteGroup();
		byte[] randomStringBytes = randomStr.getBytes(CHARSET);
		byte[] plainTextBytes = plainText.getBytes(CHARSET);
		byte[] bytesOfSizeInNetworkOrder = number2BytesInNetworkOrder(
				plainTextBytes.length);
		byte[] appIdBytes = this.appidOrCorpid.getBytes(CHARSET);

		// randomStr + networkBytesOrder + text + appid
		byteCollector.addBytes(randomStringBytes);
		byteCollector.addBytes(bytesOfSizeInNetworkOrder);
		byteCollector.addBytes(plainTextBytes);
		byteCollector.addBytes(appIdBytes);

		// ... + pad: 使用自定义的填充方式对明文进行补位填充
		byte[] padBytes = PKCS7Encoder.encode(byteCollector.size());
		byteCollector.addBytes(padBytes);

		// 获得最终的字节流, 未加密
		byte[] unencrypted = byteCollector.toBytes();

		try {
			// 设置加密模式为AES的CBC模式
			Cipher cipher = Cipher.getInstance("AES/CBC/NoPadding");
			SecretKeySpec keySpec = new SecretKeySpec(this.aesKey, "AES");
			IvParameterSpec iv = new IvParameterSpec(this.aesKey, 0, 16);
			cipher.init(Cipher.ENCRYPT_MODE, keySpec, iv);

			// 加密
			byte[] encrypted = cipher.doFinal(unencrypted);

			// 使用BASE64对加密后的字符串进行编码
			return BASE64.encodeToString(encrypted);
		} catch (Exception e) {
			throw new RuntimeException(e);
		}
	}

	/**
	 * 检验消息的真实性，并且获取解密后的明文.
	 * <ol>
	 * <li>利用收到的密文生成安全签名，进行签名验证</li>
	 * <li>若验证通过，则提取xml中的加密消息</li>
	 * <li>对消息进行解密</li>
	 * </ol>
	 *
	 * @param msgSignature 签名串，对应URL参数的msg_signature
	 * @param timeStamp    时间戳，对应URL参数的timestamp
	 * @param nonce        随机串，对应URL参数的nonce
	 * @param encryptedXml 密文，对应POST请求的数据
	 * @return 解密后的原文
	 */
	public String decrypt(String msgSignature, String timeStamp, String nonce, String encryptedXml) {
		// 密钥，公众账号的app corpSecret
		// 提取密文
		String cipherText = extractEncryptPart(encryptedXml);

		// 验证安全签名
		String signature = SHA1.gen(this.token, timeStamp, nonce, cipherText);
		if (!signature.equals(msgSignature)) {
			throw new RuntimeException("加密消息签名校验失败");
		}

		// 解密
		return decrypt(cipherText);
	}

	/**
	 * 对密文进行解密.
	 *
	 * @param cipherText 需要解密的密文
	 * @return 解密得到的明文
	 */
	public String decrypt(String cipherText) {
		byte[] original;
		try {
			// 设置解密模式为AES的CBC模式
			Cipher cipher = Cipher.getInstance("AES/CBC/NoPadding");
			SecretKeySpec key_spec = new SecretKeySpec(this.aesKey, "AES");
			IvParameterSpec iv = new IvParameterSpec(
					Arrays.copyOfRange(this.aesKey, 0, 16));
			cipher.init(Cipher.DECRYPT_MODE, key_spec, iv);

			// 使用BASE64对密文进行解码
			byte[] encrypted = Base64.decodeBase64(cipherText);

			// 解密
			original = cipher.doFinal(encrypted);
		} catch (Exception e) {
			throw new RuntimeException(e);
		}

		String xmlContent, from_appid;
		try {
			// 去除补位字符
			byte[] bytes = PKCS7Encoder.decode(original);

			// 分离16位随机字符串,网络字节序和AppId
			byte[] networkOrder = Arrays.copyOfRange(bytes, 16, 20);

			int xmlLength = bytesNetworkOrder2Number(networkOrder);

			xmlContent = new String(Arrays.copyOfRange(bytes, 20, 20 + xmlLength),
					CHARSET);
			from_appid = new String(
					Arrays.copyOfRange(bytes, 20 + xmlLength, bytes.length), CHARSET);
		} catch (Exception e) {
			throw new RuntimeException(e);
		}

		// appid不相同的情况
		if (!from_appid.equals(this.appidOrCorpid)) {
			throw new RuntimeException("AppID不正确");
		}

		return xmlContent;

	}

	public static void main(String[] args) {
		WechatCryptUtil wx = new WechatCryptUtil("RPQLqJadlaXcrhbt", "asasasasasasasasasasasasasasasasasasasasasa",
				"wx654915c3515719ea");
		String content = "28viJ9rxsFyDLAS/odx/niA72mli1tRDylfqUiloCHZNq5NagFHnccF/JlW8VAO+wuBkW7Z7avBTBJ2/qZusIwDFnCJegt2wIwj0RpH4FlRdM9WWHmInfLLO79k3fcJzqyM2vhkd71b6YnxMCuRZQMegGIHwNA4f1ghyAIT20UifNNsB5QaydGujkLK459EDIRckEYv7DTHFux0D596IM1mX0TK8vxbTS/glfKtZnf9nxkAiuj1rQ5XUE+rBq01Hdw91l5WhwBZUnHY2CKBp1OPw5twVZHemMUhTZhSPgRKA+kmjDPvkDb8KFZvscnW8pB/obkzIAZimc05VNMkobC3BJBWMZcq5CkypAnvcZdy4O2Th5YhUq6kX1VetN45hDWftA5yFdEJ1RhyeXQS1lEWUyCSZiTrCfyjqQGYLojBV30CBcbueDk4lPYJpMOUAdHznbc48D8OLjNy/W4ViwA==";
		System.out.println(wx.decrypt(content));

	}

}
